That no, boy/girl twins can NOT be identical. The standard question after learning my twins are boy/girl is, are they identical? I always reply nicely that, no, they aren't, but I've had a few people ask me if I'm sure!
I just had to tell someone that on Thursday. I was relating a story from my childhood with two identical twin girls. One of the girls has a name that is often male, but just as often female. The story itself was about a situation involving their dresses for a school event. It involved a description of ruffles, hem length, and Mary Jane shoes, PLUS the critical factor that these were IDENTICAL twins who pulled a switcheroo. At the end of it, this person looked at me in confusion and said, "But how come people didn't notice the boy wasn't a boy any more?"
Head meet desk. I said, "Like I said they were IDENTICAL twins. Girls. Hence, the dresses, etc."
Her: "But you said one of them has the [gender neutral name]."
Me: "Yes. And the owner of that name was a girl, hence the dresses, etc. But the main point is that they were IDENTICAL twins. You don't have identical twins if you have a boy and a girl."
Her: "Sure, you do. They're identical except for their sex."
Me: head meet desk again. "Then they're NOT identical. Identical means the same in every way."
Her: "Really? I always thought that identical meant almost the same except for one or two differences."
Me: "No. That would be SIMILAR."